JP2001048566A - Manufacturing method of optical fiber preform - Google Patents

Abstract

(57) [Problem] To provide a method for manufacturing a base material for a dispersion-shifted optical fiber having a large mode field diameter. SOLUTION: In an optical fiber in which a refractive index distribution is a center core 1, a side core 2, and a clad 3 in the descending order of the refractive index, a glass fine particle layer to be the center core 1 has a refractive index other than SiO _2. And the porous glass base material is made of V so that the glass fine particle layer to be the side core 2 is substantially only SiO _2.
Synthesis is performed by the AD method, and then at least one of the dehydration treatment and the sintering treatment is performed in an atmosphere containing a dopant for increasing the refractive index, and thereafter, a glass fine particle layer to be the clad 3 is formed outside thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an optical fiber preform, and more particularly to a method for manufacturing an optical fiber preform for obtaining an optical fiber having a large mode field diameter.

[0002]

2. Description of the Related Art As a method of manufacturing an optical fiber preform, VA is used.
A manufacturing method using the D method is widely used. This manufacturing method uses a raw material gas (SiCl ₄ and GeCl ₄ ) in a flame.
Is subjected to a hydrolysis reaction to grow a cylindrical porous glass base material in the axial direction. Thereafter, the porous glass preform is heated in an atmosphere of helium gas or the like to perform a dehydration process and a transparent sintering process, thereby obtaining an optical fiber preform.

A dispersion-shifted optical fiber suitable for long-distance large-capacity communication has a low dispersion (for example, ± 5 ps / n) at a wavelength around 1.55 μm where the loss of a silica-based optical fiber is the lowest.
m / km), for example, as shown in FIG. 1, a step-like refractive index distribution shape composed of a center core 1 having a relatively high refractive index and a side core 2 having a relatively low refractive index. Having. Thus, the refractive indices of the center core 1 and the side cores 2 are higher by about 1% and 0.2% than the cladding 3, respectively. The base material for the dispersion-shifted optical fiber is mainly composed of SiO ₂ . Hereinafter, an example of the manufacturing process will be described. First, as a dopant for increasing the refractive index, for example, a porous glass base material composed of a glass fine particle layer to be a Ge-doped center core and a glass fine particle layer to be a Ge-doped side core is formed. After the glass base material is subjected to a dehydration treatment and a transparent sintering treatment, a non-doped glass fine particle layer to be a clad is grown on the outside thereof, and the glass base material is subjected to a dehydration treatment and a transparent sintering treatment.

[0004]

In a dispersion-shifted optical fiber having a step-like refractive index distribution, it is necessary to increase the mode field diameter in order to suppress the occurrence of a nonlinear phenomenon. The ratio of the side core diameter / center core diameter (in FIG. 1, D ₂ /
D ₁ ) must be increased.
However, when Ge is doped into the glass fine particle layer to be the side core in the state of the porous glass base material, the glass fine particle layer tends to be softened. This is G
It is presumed that doping with e weakens the bonding between the glass particles. For this reason, when the glass fine particle layer to be the side core is made thick to increase the ratio of the side core diameter / center core diameter, there is a problem that the glass fine particle layer to be the side core is cracked in the VAD synthesis step.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a glass fine particle layer to be a center core having a relatively high refractive index and a side core having a relatively low refractive index. A porous glass base material having a glass fine particle layer to be synthesized is synthesized by a VAD method, and then the porous glass base material is subjected to dehydration treatment and sintering treatment. In the method for manufacturing an optical fiber preform for forming a glass fine particle layer to be a clad having a lower refractive index, the glass fine particle layer to be a center core includes Si.
The glass fine particle layer which is doped with a dopant for raising the refractive index in addition to O ₂ and which is to be a side core is substantially made of SiO ₂
The porous glass base material is synthesized by the VAD method so that only a dehydration process or a sintering process is performed in an atmosphere containing a dopant that increases the refractive index. It is characterized in that a glass fine particle layer to be formed is formed.

The present invention has been accomplished as a result of intensive experimentation. That is, as described above, when the porous glass base material is grown without doping the dopant into the glass fine particle layer to be the side core, the glass fine particle layer to be the side core does not soften, and therefore, the glass core layer to be the side core should be formed. Even when the diameter of the glass fine particle layer is increased, it is possible to prevent cracks from entering the glass fine particle layer which is to be a side core when synthesizing by the VAD method. Further, when the dehydration treatment or the sintering treatment is performed in an atmosphere containing a dopant for increasing the refractive index, the refractive index of the glass fine particle layer to be a side core can be increased. Therefore, according to the method of the present invention, it is possible to manufacture a preform for a dispersion-shifted optical fiber in which the ratio of the side core diameter / center core diameter is increased (therefore, the mode field diameter is large).

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for manufacturing an optical fiber preform according to the present invention will be described below. The steps of the manufacturing method are as follows. 1) First, a glass fine particle layer to be a center core made of GeO ₂ (dopant for increasing the refractive index of glass) and SiO _2, and a glass fine particle layer to be a side core made of substantially only SiO _2. A porous glass base material is synthesized by a VAD method. 2) Insert the porous glass base material into a quartz furnace tube surrounded by a resistance heating furnace, and heat to 1100 to 1300 ° C in a mixed atmosphere of helium, oxygen, and thionyl chloride (a dopant that increases the refractive index of glass). To perform a dehydration treatment. 3) Next, sintering is performed by heating to 1400 to 1600 ° C. in a mixed atmosphere of helium and thionyl chloride. 4) Thereafter, a glass fine particle layer to be a clad is synthesized by an external method, and dehydration processing and transparent sintering processing are performed again. In this case, the relative refractive index difference between the center core and the side core with respect to the clad is 0.5 to
1.0% and 0.2 to 0.4%.

From the optical fiber preform thus manufactured, a center core diameter of 3 μm and a side core diameter of 18 μm were obtained.
m, and thus a dispersion-shifted optical fiber having a side core diameter / center core diameter of 6 was obtained, and its mode field diameter was 9.5 μm. Incidentally, the optical fiber obtained from the optical fiber preform manufactured by the conventional manufacturing method has a center core diameter of 3 μm and a maximum side core diameter that does not cause cracks of 13.5 μm. The diameter was at most 4.5. The mode field diameter of the dispersion shifted optical fiber having the maximum side core diameter / center core diameter was 8.5 μm. As described above, when the optical fiber preform according to the manufacturing method of the present embodiment is used, the dispersion-shifted light having a mode field diameter larger than the dispersion-shifted optical fiber obtained from the optical fiber preform manufactured by the conventional manufacturing method. Fiber can be manufactured. Although thionyl chloride was used as a dopant for increasing the refractive index during the dehydration treatment or the sintering treatment, any type of substance can be used as long as it can exert the same effect as the present invention.

[0009]

As described above, according to the present invention, there is an excellent effect that a preform for a dispersion-shifted optical fiber having a large mode field diameter can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a refractive index distribution shape of a dispersion-shifted optical fiber.

[Explanation of symbols]

 1 Center core 2 Side core 3 Clad

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H050 AA01 AB04X AB05X AC28 AD00 4G021 CA11 EA01 EB01 EB13

Claims (1)

[Claims] 1. A center core having a relatively high refractive index.
Glass layer and the refractive index
Porous glass base material with glass fine particle layer to be formed
Is synthesized by the VAD method, and then the porous glass base material is synthesized.
After dehydration and sintering,
Lower than the refractive index of the core and the side core.
Glass particle layer to be a clad with high refractive index
In the method for manufacturing an optical fiber preform to be formed,
The glass fine particle layer to be the core is made of SiO_TwoBesides
Doped with dopants that increase the folding ratio to become side cores
The glass fine particle layer to be formed is substantially SiO 2 _TwoOnly
The porous glass base material is synthesized by the VAD method
At least one of dehydration treatment or sintering treatment
In an atmosphere containing a dopant that increases the refractive index.
After that, the glass fines to be clad
Production of an optical fiber preform characterized by forming a particle layer
Construction method.